Inkjet printers may use a printhead to eject ink droplets positionally onto print media such as paper. The printhead may include a plate having an array of bores or orifices, known as an orifice plate. The orifices may function as nozzles at which ink droplets may be created as ink is expelled from the printhead through the orifices. An array of thin-film electronic devices, such as resistor heaters or piezo elements, also may be positioned adjacent the array of orifices in the printhead. Selective energization of such thin-film devices may enable selective ejection of ink droplets from corresponding orifices.
The arrangement of orifices within an orifice plate may play an important role in determining print quality. In particular, the density of orifices may define the density of droplets that may be delivered to the print media. For example, orifice plates may include a pair of side-by-side orifice columns, each having 300 orifices per column-inch, which is equivalent to a center-to-center nozzle spacing of about 84 micrometers. The columns may be offset lengthwise along the axis of the columns by one-half orifice spacing relative to one another within the orifice plate to enable printing 600 droplets (or dots) per inch (dpi).
To achieve even higher printing resolutions, orifice plates with a higher density of nozzles may be needed. For example, printheads with orifice plates having densities of 600 nozzles per column-inch in a pair of adjacent, offset columns may deliver a total of 1200 dpi, to offer twice the printing resolution of 600 dpi printheads. However, the orifice plates of such higher resolution printheads may be difficult to fabricate.
Orifice plates may be fabricated by electroformation on a mandrel. The mandrel offers a conductive surface onto which a layer of metal may be electrodeposited to create a body portion of an orifice plate. The conductive surface may be interrupted by nonconductive islands that do not promote electrodeposition. Accordingly, the layer of metal may grow around and/or over the nonconductive islands to define orifices at the positions of the islands.
Mandrels with nonconductive islands in the form of pillars may define orifices by electrodeposition around the pillars. Accordingly, the pillars may be shaped according to the desired structure of the orifices, for example, by using a complementary mold to create the pillars. Recesses complementary to each of the pillars may be formed in the mold. Next, the recesses may be filled with a flowable material, and the flowable material solidified. Then, the solidified material may be separated from the mold to expose the pillars. A conductive surface may be formed on the surface between the pillars, before or after separation of the pillars from the recesses, to complete the mandrel. However, the use of a mold to create mandrel pillars may be unsatisfactory for fabricating mandrels with the high densities of thin pillars often needed for higher resolution orifice plates. In particular, the thin pillars may break when they are separated from the mold. In addition, the recesses may not be filled consistently with the flowable material, so that many of the pillars may be defective in structure.
Mandrels with nonconductive islands also may define orifices by electrodeposition over the pillars. In this approach, the body portion of the orifice plate may thicken and grow laterally over the perimeter of the islands at approximately the same rate. Accordingly, an orifice may be formed in a central region over each island, with the island itself defining a counterbore of the orifice plate that adjoins the orifice. As the body portion of the orifice plate grows thicker, the orifice decreases in diameter. Accordingly, forming a high density of orifices with sufficient diameters may require closely spaced islands and electrodeposition of a very thin body portion. However, the resultant orifice plate may be too thin to be useful, and the shape of the orifices may be difficult to modify.